Many food products contain varying amounts of oil, i.e., liquid triglycerides, which can be extracted as a valuable commodity. Such food products include cocoa and other plant materials, such as oil seeds, cereal brans, fruits, beans, and nuts. There are numerous important commercial uses of the oils derived from such plant materials, such as in cooking, cosmetics, pharmaceuticals (as carriers), lubricants, and other applications. Depending on the food product, the defatted food product might also have some commercial or industrial use. Accordingly, numerous processes aimed at extracting and separating such oils have been proposed.
Organic solvents are frequently used as the medium for extracting oil from such food products. In a conventional extraction process, the oil-bearing food product is treated with a suitable solvent, usually a lower carbon alkane, such as hexane, to extract the oil from the oil-bearing food product. The resulting solvent/oil mixture, called a "miscella," is then separated in a distillation unit to separate the oil product from the solvent, which is recycled.
U.S. Pat. No. 2,680,754 to Stapelberg is directed to the extraction of oils and fats from solids which are placed in an extractor. A number of tanks store miscella of increasing purity from a previous batch process. To start the operation, miscella from the tank which contains the least pure miscella (i.e., the highest oil content) is introduced to the extractor. During the extraction process, miscella of increasing purity is sequentially delivered to the extractor until substantially pure solvent is used. Between batch extraction processes, the defatted solids are conveyed to a bin, and the solvent remaining in the defatted solids is recovered, subsequently purified, then condensed and returned as fresh solvent to the fresh solvent tank.
While prior art extraction methods have met with various degrees of commercial success, there still remains a need for an improved solvent extraction method which is more energy and cost efficient, which can effectively and easily remove the solvent from the defatted solids, and which efficiently recycles the solvent.